This type of machine comprises a fixed platen and a mobile traverse which nears and distances from the fixed platen on a horizontal axis.
Each of the two members, the platen and the traverse, bears a half-die provided with one or more moulds destined to combine perfectly with the mould of the other half-die.
The fixed platen bears a fixed half-die which is associated with precision to a nozzle which injects the plastic material in the molten, liquid or pasty state.
Each of the two members, the platen and the traverse, has a plate-shape and bears a series of threaded holes, generally at least two in number, more often six, which serve to fix the half-die to the member by means of a screw.
The fixing operation of the half-die to the member is very laborious, and comprises positioning the half-die on the member, inserting and fastening the screws of the respective holes, thus performing a pre-tightening, nearing the two half-dies up to achieving a perfect combination, and then performing the final tightening.
This operation, very costly in terms of time, has to be repeated each time the die is to be changed, which, given the high productivity of this type of machine is done with a certain frequency and implicates long down times which have a negative influence on productivity.
Thus the problem of realising a fastening system of the half-die to the traverse and platen of the press which involves only short operating times while preserving the necessary precision of fixing is very relevant.
General rapid fastening means are known in the prior art, described for example in document U.S. Pat. No. 6,244,780.
Document U.S. Pat. No. 6,244,780 relates to the fastening of a cutting tool to a respective activating spur, and exhibits no problem of orientation of the tool in relation to the support.
The fastening devices described in this document comprise two parts destined to be separately associated to the pieces to be assembled.
A first part comprises a threaded spur screwed into a hole present in one of the two pieces to be assembled.
The spur has a cylindrical portion that projects from the surface of the piece, which portion is destined to insert in a complementary first hole present in the other part to be assembled.
The external surface of the cylindrical portion comprises first parallel channels having a triangular section and a constant pitch, and a seating parallel to the axis which separates the cylindrical part into two symmetrical appendages.
A second part comprises a sort of clamp suitable for being associated to the other piece to be assembled and destined to clamp the projecting part of the first part.
The second part exhibits a first hole for receiving the appendages and a second hole opening externally of the piece.
The second hole exhibits an axis which intersects the axis of the first hole and is destined to receive a through-bolt having an end destined to screw into a first nut snugly inserted in the second hole, and to slidably house a second nut similar to the first.
The two nuts are connected by a single bolt which, when the parts are assembled, is located in the seating.
The nuts have facing surfaces thereof provided with triangular-section channels complementary with the external channels of the appendages of the cylindrical portion.
The assembly of the two parts is obtained by screwing the threaded spur into the complementary hole present in one of the two pieces to be assembled, by inserting the appendages projecting from the spur into the complementary hole present in the other part, and tightening the two nuts connected by the bolt up to co-penetrating the channels thereof in the channels of the appendages.
The orientation of the spur in the hole in which it is screwed is entirely random, as will be the reciprocal orientation of the two pieces.
The above-described fastening devices exhibit the drawback of not being able to guarantee perfect blocking of the spur in the respective hole, and thus maintaining the desired reciprocal orientation between the two assembled pieces, since the two appendages deriving from the spur have to have an orientation which is compatible with the orientation of the axis of the second hole opening externally of the piece.
The structures of the prior art are not suitable for application where there is a need for a perfect fastening of the spur, respective a compulsory orientation between the two parts to be assembled.
The problem increases when at least two fastening devices are to be provided between two parts to be assembled.
The structures of the prior art are in particular unsuitable for fixing a half-die to the mobile traverse of a press, as the half-die has to be fixed to at least two points to the traverse by means of two fastening devices having different and predetermined orientations.
Examples of such fastening devices, according to the preamble of the claim 1, are described in DE 33 31 676 and in U.S. Pat. No. 5,078,586.